52 THE STRUCTURE OF FLOWERS. 



insect alights on one or two petals. In order to support it, 

 an immense gain is secured if the flower can call in the aid 

 of the other petals ; and this is obviously obtained by their 

 cohesion into a tube, just so far as the required strength is 

 wanted. Nothing would be gained by the portions of the 

 limb being united, as far as additional strength was required 

 to bear the bux'den. The tubular structure is the strongest 

 possible, and when short, as in rotate corollas, little extra 

 aid is required ; but if it be long and visited by heavy insects 

 and not by Lepidoptera, which hover in front of the flower 

 and only insert their long and slender proboscides, then the 

 tube finds additional support in the calyx being tubular as 

 well. At other times mutual support is gained by the close 

 contact of the flowei^s, as in a capitulum of the Compositce, 

 from which the calyx vanishes. 



Of course, every degree conceivable is met with between 

 short, stout, and strong tubes with no additional aid, and 

 slender ones supported by a strengthened gamosepalous calyx. 

 These are adapted to insects which alight upon the corolla 

 limb ; while for Lepidoptera the tube is more elongated, and, 

 as no weight is thrown on the anterior petals, no extra 

 support is required. That this is the true intei'pretation of 

 the origin of a gamopetalous coi-oUa, appears from such 

 negative evidence as is seen, for example, in Lonicera Peri- 

 chjmenum and Asperula taurina* which have greatly elongated 

 and contracted tubes, deriving no siipport from the arrested 

 calyx ; and although somewhat two-lipped, the anterior 

 member is no larger than the others ; the reverse being 

 always the case when a heavy insect is the regular visitor. 

 These two species are exclusively fertilised by the Lepidoptera, 

 such as the Hawk-moth, which only hovers in front of the 

 orifice, but throws no weight upon the corolla. 



* See Miiller's fignres, Fertilisation, etc., pp. 296, 303. 



